Process for refining oils



Dec. 26,1944.l F. APGAR 2,365,993

n PROCESS FOR REFINING OILS Filed Jan. 24, 1944 P 'w TTORNEYS Patented Dec. 26, 1944 implication January 24, 1944, seal No; 5193565 reclaim. tontas-29) prove'dJprocessiforitherening of petroleum distillates, such as gasoline, containing undesirable sulfur compounds, WK"sucl'i as mercaptans.

The presence dfimercaptans "in gasoline was difensive odorfand corrosiven'ature. Petroleum 'distillate'scontaining such Iobjectionable 'sulfur '-compouns are :known as s'ourv distillates and *the;p1oc'ess pf ifreeing `sour distiilates of these sulfur compounds :is known sweetening The Jsvveetening of Vthese sourjpetroleum 'distilment" has lbeen Vgenerallyfregarded as the mo'st Jcalled fdoc'tor solution? 'at "or `near atmospheric Ytemperature. Atypical doctor."solution is 'one llgorotluced":by"admixing124pol1nds of "caustic soda, lIl!) rpounds'fo'f litharge and 125 `gallons of water. I'he amount ofthissolution added to `the Vo`il"is 'usually` preuetermined *by :tests ink which` addi- `tional""doses 'aire ."added "to fa 'Sample `of 'the distillate'r until'it-:ldoesgnot"further Ydarken. Y Almost "invariab1y-elemental sulfur has ,been .'nally.- addfed Ato the :distillate to 'complete -.the `d'ocztor ibreakl In-"such operation, Icare must beftaken to favoid adding Vexcess sulfur 'as 'the presence of sulfur renders thenished distillate corrosive.

"Ih'oug'h jtlie"doctjor'treatn'-1ent 'is 'generally e`f festive-in sweetenng sour distillates, it hasbeen found to have disadvantages with respect to the reiining of modern gasolinemotor fuels. Specically, gasoline so sweetened has been, found. to be ,impaired .as to its. antifknock properties, as toits susceptibility totimprovement `of its. antiknock valuesiby `theaddition of tetraethylflead,

i hereinafter .referred to 4as'T. E. L., and .as toits susceptibility totfthe actionof oxidation inhibitors` ofthe .typeirequently added tto fini-prove stability instorage. Particularly `in ,present-day motor .ueL `anti-knock properties and :susceptibility to improvement thereof 4bythe addition .of T. E. L., are of major importance and it isa'n objeotvof the present invention to provide aprec- -ess whereby zone may .economically :effect -the zsweetening` of the zgasoline without impairment subsequently 'appear therein, "are attained by Vrrny yimproved process The process "ffof Nmy 'present `'invention 'consists Iprimarily of two majorstepsor stages. liTnthe "brought "into intimate contact with *an aqueous "suspensionidf'fcadmium 2hydroxide 'at anielevaited vten'lperfatture andWithTigid vexclusion "of air v"or otherfoxygenecontaininggases In the second thas been""separaited fromfthe ma'jor portion of "thefoul'ed treatingcompound,` is intimately fcon- "tac'te`d, also'at fan 'elevated temperature,` `'with "an `oxygen#corn'airiing 44gas -such jas ai Hdvantageouslm "the 'cadmium *hydroxide "is 'suppliedv to the "'firststage "of the 'operation as a suspension in a caustic solution. "Acaustiesoda solution dof `such :concentration as to have a "Baume'-'g`ravity of "romabout"ill0 to 'about-30 20 4and containing cadmium "hydroxide 'in suspen- "fu mium'mercaptidesjas indicated v'by the 'following equation: n

(i) 2RsH+ca oH aamsizcdetrao `verliere R, yrepresents" a`-``-hydrocarbon'fradical.

lmarilyf `tnoonflili'e` amount of Lmerc'aptans lpresent `iii-fthe"distillate'to besweetened and'xnaylbe readl'lilycalculatedlfrom-lthe fab'ove Equation `1. fanonnt lofl cadmium t'gliydfroi'ide somewhat' in 'e'xam cess of the theoretical-requirement is usual'lynle- 'sirable.

fthe TirstI-s'tage*ofV my process, 'the major "portionf=oi"-ithe @sulfur present Ainf'the distillate fc'hargedf'thereto is-separated =fror`n 'the partially 11215 ftre'atedi distillatelas'l cadmium `meicaptides, which are substantially@insoluble Vin hydrocarbons. :Howeverfa fniinor-poition-'dfl the Lm'ercaptides re- `-main in 'the idistiil-late. The partially-treated 'dis- -ftilla-te *from thel first Stage "of )my g process fis Vnot v15() impairedas incanti-knock properties, stability o'r susceptibilityto"improvement o`f its anti-'knock yaluesibyfftheaddition offlTjE. `L."? The major ,portion 'of Lthe gsulfurhas'been .removed ybut the distillatefisndttconpltely norfsuicientlysweet- "-thereof. .fobj'ectfandlfother--advantages fas ies Acned, "because 'oi *traces 'of mercaptides remain- A liquid phase.

vhave had no commercial signicance.

ing either in solution or suspended therein. To effect the desired sweetening, it is essential that the residual objectionable sulfur compounds be eliminated from the oil and this is accomplished in the second stage of my process without sacrice of the advantages obtained by' the first stage of the process with respect to other desirable properties.

In the second'stage'of my process the traces of mercaptides remaining in solution and in suspension in partially-treated distillates are converted to disuldes by intimately contacting the partially treated distillate with air, or the like, at an elevated temperature. The reaction by which the mercaptides are converted to disulfides may be represented by the following equation:

The disulfides formed by this reaction have substantially the same effect upon the octane number of the oil as the mercaptides from which they are formed and thus the improvement in T. E. L. susceptibility obtained by the rst stage is retained.

An essential characteristic of my improved process is that each of the operations be carried out at an elevated temperature and under a pressure sufficient to maintain the distillate in the The pressure employed will depend upon the characteristics of the oil being treated and the operating temperature, The temperature of the operation may be varied somewhat but, in order to effect the reaction within a reasonable period of time and to obtain maximum benefits, it is desirable to maintain the temperature of each stage of the treatment within a range of about 180-260 F.

The use of cadmium hydroxide in the sweetening of sour distillate has previously been proposed in an operation carried out at atmospheric temperatures and pressures and Without recognition of the effects of air upon the results obtained. So far as I am aware, such previous proposals Serious difficulties previously encountered included the adequateA separation of the mercaptides from the treated distillate and the regeneration of the fouled treating solution.

The process of my present invention is distinguished from such previously proposed operations by a sequence of correlated steps carried out under the herein-described conditions. The desired sweetening of the distillate in conjunction with the desired improvements in anti-knock characteristics, susceptibility to T. E. L. and improvements in gun stability will not result from either of these process steps alone, but these advantages are readily obtained by the correlation of the steps of my process when carried out under the conditions herein described.

I have found that these advantages are not obtained when air, or other oxygen-containing gases, is present in the first stage of the treatment. Accordingly, a further essential of my improved process is the rigid exclusion of air from the first stage of the operation.

A further aspect of my present invention is the regeneration of the fouled treating solution or suspension separated from the first stage of the operation. Cadmium hydroxide is relatively expensive and, accordingly, from a practical aspect, it is essential that it be recovered for repeated use. My present invention provides a unitary process whereby the cadmium in the form of mercaptides, precipitated from the first stage of the operation, is readily and economically reconverted to cadmium hydroxide which may be returned to the rst stage of the operation. The regeneration of the cadmium hydroxide is effected by blowing the fouled treating solution, separated from the first stage of the operation, with air, while maintained at the boiling temperature of the solution. This regeneration may with advantage be carried out at Aabout atmospheric pressure.

The invention further provides an improved process which may with advantage be carried on continuously by the continuous supply of the sour distillate and cadmium hydroxide to the first stage of the operation with the exclusion of air, separation and continuous withdrawal of the partially-treated distillate and fouled treating solution on the first stage, continuously subjecting the partially-treated distillate to treatment with air in the second stage of the operation and the continuous'regeneration of the fouled treating solution and return of regenerated cadmium hydroxide to the first stage of the operation.

The invention will be further described and illustrated by reference to the accompanying flow diagram which represents an advantageous method by which the process may be continuously carried on. In this method of operation the raw distillate, which for instance, may be stabilizer or debutanizer bottoms devoid of air and having its temperatures adjusted to about 180260 F., is

` passed to the system through the line I. Caustic soda solution having cadmium hydroxide suspended therein, and advantageously. at approximately the temperature of the distillateis introduced into the system through the lines 2a and 2, is combined with the raw distillate in line l and passes together therewith through the mixer, conventionally indicated at 3. The mixer l may with advantage consist of a series of oriiice plate mixers whereby the distillate and treating solution are intimately admixed. From the mixer the admixed distillate and treating solution pass through line 4` into the chamber 5 which, on the flow sheet, is designated 1st stage treating tower.

The mixture is preferably introduced into the lower part of the tower 'at a point spaced from the bottom so as to provide a relatively quiescent zone at the bottom of the tower to facilitate the separation of the distillate from the fouled treating solution. The mixture may be introduced into the tower as indicated or with advantage through a spray head, not shown. Within this tower the distillate is separated from the treating solution by gravity and passes from the top of theftower through the line 6.

In the operation of the rst stage treating tower, as just described, the admixed treating solution and sour distillate flow generally concurrently through the tower, the spent treating solution settling out inthe bottom of the tower. An alternative arrangement which may be used with advantage is to pass the raw distillate, unmixed with the treating solution, directly into the lower portion of the tower and introduce the treating solution into the upper portion ol the tower so that they pass through the tower in intimate contact in a generally countercurrent direction.

This alternativemethod of operation may be carried out in the apparatus diagrammatically represented in the drawing by closing the valve in line 2 nearest the juncture with line I 'and passing'fi thesztreating:zvsolution: directlyV intofithe upper part of the towemthroughillinei2f?. With thief-arrangementthearawldistillatefimay belbytherproper adjustment ot thavalves showmand `fronrrthenceglirectiyfintoithe lozwerlportionl'of4 the towers" through` linee dfrwithout: tprevious: .mixin' with the:treatingzsolution.V l 1 the'fdiawing iat -Ifgftheliquidslevel preferably .being maintained `fnear. the.:` iupper. .endl or ithe; chamber asfsindicated... x

The:"fouled.A iti-eati'nglisolation,.fl` separated :from

` the .dttsillate ln .the.1.chamber' his; withdrawn therefrom through 'line .sito ar-regeneratingf system subsequentlyvdescribed.hereini= l Thefabove-describedftreatment oftherawdistillateiawith the'y cadmium?.hydroxidesuspension constitutesffthe. rststage Aoft my processi Raw distillate.passingfto:thisrrsttstageaoi thefprocess is free-:tromair ori'oxygenifandlnm air or'. oxy'- ygens-is .permitted-io.' comedn c'ontact-rwith dis- `tilllate duringithisstageLof the operation.` Pressure is maintainedinon the s` systennA sufficientto maintain. therfdistillatef 1in sliquidl :'phaseland.. .the temperature, concentrationV of treating:A solution and ratioy of' fcadmium hydroxidetto` distillate# are maintained asf previously. indicated. The distillate passing ffromtheupper lendloi. the chamber f i through1 line l `1 is only partially: sweetened and'zusually contains .al minor, thoughundesirable portion; of nrer'captides,-rparticularlycadL miummercaptides. i y

As thislpartiallyLsweetened distillateipasses 1undei`-` pressure from lthef lirst listage-A oif the operation through .line zltothe second` stage ofrthe operatiomairis injected into .itllthrough linezll. The Amixture on distillate: andoairV then'. passes thro ugh the. mixer l l il, which. may fwith advantage bei of -1 the type. previously` described;` andxinto chamber il. whichglonthef flow.l sheet, is..desig; nated 2ndstage settler.v The air. entering this second .stage ot vthe.'operati'onf.will.,. of. cours'e,;b'e under. pressure: andm'ay be supplied. from any convenient' source.. l .Aspreviouslyf notedr. the .cadmium mercantili-es reactwith the airin .the secondlstage of the operation: forming cadmium hydroxide and disulhcles.'v The .cadmiumz'hydroxide thus Vformed an'dcany. treating. solution entrainedtfrom. the

1 towen'. are.permittedrto. settle out from thedis- "tillatexin the4 chamber ll` and. are discharged therefrom. through line I2,A controlled by valve l3-,. andfiline- I 4 :to: the. regenerating; system sub.- sequently to. be .'described.

' The. set-nerll iswithadvantage. of -sucnsize and shape as to permit adequate settling and separationpof.. the cadmium hydroxide, formed byr aotionooil the:.air, and any entrainedftreating solution from the distillate: and. `for this reason it...fis::desirable to. maintain. a l. considerable Volumecof distillateinlthe settler.. In the apparatussrepresentem.:theliquid level in the. chamber Il.J may'.` beA observed: by` means.` of the gauge glass' I5..v By. observing: these precautions,. a. sweettandsubstantially clarified.,distillateamay be-. discharged. from:..thefV upper 4portion of" the agradece obtainedtisido'ctor;- sweetpshavingiimproved; anti;

knock characteristics'.andfsusceptibilityztolTJIELtL. andtimproved: vstability.'` with: respectftcutgunufor# mation.V

. As previously indicated, a particularlyfdesirable aspectiioff'the invention is .an operation: which includes the regeneration of the cadmiumhy.- droxicle and its repeatedfluse. In such operation the .fouled treating-solution withdrawn from the treating tower through lines 8 and l'd, and advantageously also the materialsettled from-the distillate inthe chamber Il, are passed tovasifpre'- heater l1 wherein the cadmium mercaptide-conftainingfmaterial is. heated to its .boiling pointaas by means of the steam coil shown; an'd'irom thence passes through linelintofthe upper'portion of thetower l 9;

In .passing downwardly throughv thetower, 'whichis advantageously bellied, as'fishown; the heated.y fouled solution is intimately contacted with air introduced into the bottomof the tower through linei2ll. -Toinsure adequate contactbetween the fouled solution and the air, a substantial body of the' liquid is maintained in the tower, thetower being flooded .with .the fouled solution toa. level above that ofthe entry ofline IS'into the tower, This level may loe maintained by means of an. automaticlevel control conventionally indicatedl at 2l.. l

In passing'downwardly through the 4tower-in contact with the air, .the cadmium mercaptides react W'Vith the oxygen of the air to form cadmium hydroxide and disul'ldesr The disuldes, water vapor and air pass out from the upper end` of the tower, as'shown in the diagram, and the solution containing'the cadmium hydroxide is withdrawn from the bottom of the tower through line 22 tothe mixing vessel 23, whereinzthefcadmium hydroxide is `maintained in suspension by agitation with air. or the `like'introduced. through line 24, and from which the regenerated treating solutionlis Withdrawn throughv line 25"and returned to the rst stage of the operation by means of pump 26 and lines 21' and 2.' Such operation may lloe carried on continuously with a minimumof attention and only a minorloss of cadmium compounds; Water or caustic 'solution and cadmium hydroxide, in amounts suicient to maintain the treating'suspension at-the desired concentration, may be charged to the mixing vessel 23;'` continuously: or.as;required,; byi conventional meansfrnota4 shown; on.; the diagramp The beneiits derivedfrommy improved process will. be illustrated by the following speci'o examples oflresults oi an operationzcarried.out; at operatingtemperatureof 220 F. For comparison, the characteristics of theoil prior toA treatment andof thesame oil after treatment, inA accordance with my presentinvention, are given. For further comparison, the characteristics-of the sameoil treated with a `sulicient quantity of a `standard' silver nitrate solution to remove all mercaptans as silver merc'aptides are given.

the following tabulation, the characteristics of the untreated oil are set forth in column l. In column 2 there are set forth the characteristics of the same oil .treated withfisilver nitrate vin the presence/orali for a` period-of 0.25' hour under atmospheric temperaturesandpressure. In the thirdcolurnn, there arel set forth characteristics of the oill after treatment in .accordance with my presentinvention. for thewsame period of time under a pressure of-40apounds per square. inch at a temperatureofv 220 R', anatmosphere .of nitrogen ,having beenused in:.the-1'1`.rst` stage;.0f the:` operation.. In .the` latter .operation',. thersour distillate and treating solution were used in proportions of 3:1 by volume. The treating solution was prepared by admixing cadmium chloride with a 25 degree Baum caustic soda solution in proportions of 5 pounds of CdCla per barrel of solu- 5 tion.

Table I Gravity 65. 2 55. 0 54. 9 Reid vapor pressure 5.6 5. 5. 5 Mercaptan sulfur 16.0 0. O 0.0 0. 060 0. 04 0. 043 101.0 101.0 l 100 190 190 110 113 10s 157 15s 154 284 287 284 750g. 372 074 373 End point 411 408 412 Loss Q pcrcent.. 2.0 1.5 2.0

In a further test, a sour distillate was treated in accordance with my present invention under conditions identical with those just described except that the operating pressure was 44 pounds per square inch. The characteristics of this distillate before and after treatment are set forth in the following tabulation:

Table II Before After treatment treatment 3o Gravity ..A. P. I.. 56.3 55. 8 Reid vapor pressure. 6. 4 6. l Mercaptan sulfur percent 13. 5 0.0 ur ...110.` 0.057 0.045 Iodine valu 101. 9 Stability minutes..

Octane value (Motor method):

Neat

The proportion of air used in the second stage of my process may be varied over a considerable range. Suflicient air should be used to convert all of the residual mercaptan sulfur present in the distillate to disulrldes. 'I'he optimum proportion of air will vary somewhat with other operating conditions but may readily be determined by simple tests. Itis usually desirable to use an amount of air considerably in excess of the theoretical requirement rbut, since there is a tendency for the .volatile constituents of the distillate to be carried off by the air, it is desirable to avoid the use of an amount of air in excess of that found necessary for maximum conversion of the mercaptides.

I claim: 65

1. A process for the treatment of light petroleum distillate containing undesirable sulfur compounds to eliminate the sulfur compounds therefrom comprising intimately contacting the distillate at an elevated temperature and in the absence of oxygen with an aqueous suspension of cadmium hydroxide, separating the distillate from the aqueous suspension and intimately contacting the separated distillate with air while at an elevated temperature, each of said operations being under suiiicient pressure to maintain the distillate in the liquid phase.

2. A process for the treatment of light petroleum distillates containing undesirable sulfur compounds to eliminate said sulfur compounds therefrom comprising intimately contacting the distillate at a temperature of about to 260 F., and in the absence of oxygen with an aqueous suspension of cadmium hydroxide, separating the distillate from the aqueous suspension and intimately contacting the separated distillate with air while at a temperature of about 180 to 260 F., each of said operations being under sufficient pressure to maintain the distillate in the liquid phase.

3. A process for the .treatment of light petroleum distillate containing undesirable sulfur compounds to eliminate the sulfur compounds therefrom comprising intimately contacting the distillate at an elevated temperature and in the absence of oxygen with an alkaline aqueous suspension of cadmium hydroxide, separating the distillate from the aqueous suspension and intimately contacting the separated distillate with air while at an elevated temperature, each of said operations being under sufficient pressure to maintain the distillate in the liquid phase.

4. A process for the treatment of light petroleum distillates containing undesirable sulfur compounds to eliminate said sulfur compounds therefrom comprising intimately contacting the distillate atan elevated temperature and in the absence of oxygen with cadmium hydroxide suspended in an aqueous solution of caustic soda of about 10 to 30 Baume, separating the distillate from the aqueous suspension and intimately contacting the separated distillate with oxygen while at an elevated temperature, each of said operations being under suiiicient pressure to maintain the distillate in the liquid phase.

5. A two-stage process for the treatment of light petroleum distillate containing undesirable sulfur compounds to eliminate said sulfur cornpounds therefrom, comprising, as the rst stage, intimately contacting the distillate, at an elevated temperature and in the absence of oxygen, with an aqueous suspension of cadmium hydroxide, separating the partially treated distillate from the fouled aqueous suspension and, as the second stage, intimately contacting the separated -distillate from the first stage with air While at an imating its boiling point, whereby cadmium mercaptides formed in the first stage of the operation are reconverted to cadmium hydroxide, and returning the regenerated cadmium hydroxide in aqueous suspension to the first stage of the process.

6. A continuous two-stage process for the treatment of light petroleum distillate containing undesirable sulfur compounds to eliminate said sulfur compounds therefrom comprising, as the first stage, continuously admixing the distillate, at an elevated temperature and in the absence of oxygen, with an aqueous suspension of cadmium hydroxide, continuously separating the partially treated distillate from the fouled aqueous suspension and, as the second stage, continuously and intimately contacting the separated distillate from the first stage, with air while at an elevated temperature, settling the distillate and continuously withdrawing the treated distillate from the settling zone, each of said stages beingun der sufl'icient pressure to maintain the distillate in the liquid phase, continuously withdrawing fouled aqueous suspension from the first stage of the operation and passing it to a regenerating zone wherein it is blown with air while being maintained at a temperature approximating its boiling point, whereby cadmium mercaptides formed in the rst stage of the operation are reconverted to cadmium hydroxide, and continuously returning the regenerated cadmium hydroxide in aqueous suspension to the rst stage of the process and intimately admixed it therein with the distillate charge.

- FRANK A. APGAR. 

